1. Field of the Invention
The present invention generally relates to a data transmission system with simultaneously utilizing more than two parallel data-transmission lines used in an LAN (local area network). More specifically, the present invention is directed to a data transmission method and apparatus capable of detecting erroneous data distribution in such a local area network.
2. Description of the Related Art
In the above-described conventional multi-data transmission system, a plurality of data transmission stations are coupled with each other via more than two parallel data transmission lines made of coaxial cable or optical cables. In a normal condition, these data are transmitted among the data transmission stations by simultaneously utilizing all of the data transmission lines, or alternately utilizing these data transmission lines. In the case of failure of any one of the data transmission lines, the data transmission can be continuously performed among the data transmission stations with use of other non-failed data transmission lines.
As a result, higher reliabilities on the line malfunction can be achieved in such a multi-data transmission system, as compared with the single data transmission line. This, the multi-data transmission system is generally suitable for transmitting the important data.
Such a conventional multi-data transmission system per se is known as those in the art, for instance, Japanese KOKAI (Disclosure) patent application No. 58-62949 opened on Apr. 14, 1983, filed by the same Applicant.
In the conventional multi-data transmission system, since two or more data transmission lines are employed therein, there are provided a large quantity of electronic and mechanical parts, such as coaxial cables (including optical fiber cables), connectors, cable taps and repeaters on the data transmission lines. Accordingly, great possibilities may exist in that one data transmission line is mistakenly connected to the irrelevant data transmission line due to the careless mistake by the cable joint worker, which is the so-called "erroneous data distribution".
In such erroneous data distribution, since the same data are normally transferred to all of the data-transmission lines in the conventional multi-data transmission system, each of the data transmission stations can receive these data without any problem even if the erroneous data distribution occurs in the data transmission line. In other words, there is no measure to detect such erroneous data distribution occurring on the data transmission line.
If a failure or malfunction happens to occur in the data transmission line on which the erroneous data distribution occurs, all of the data transmission stations are connected to a given data transmission line. However, even when the respective data transmission stations are attempted to be connected to the expected data transmission lines, all of the data transmission stations are not always connected to the correct data transmission lines, respectively. This causes unsatisfactory data reception.
In other words, according to the conventional multi-data transmission system, even when there is the erroneous data distribution on the data transmission line 9, normal data transmission can be performed unless there is no line failure, e.g., line interruption.
The present invention has been made in an attempt to solve the above-described problems of the conventional multi-data transmission system, and therefore has an object to provide a data transmitting method and a data transmission apparatus capable of immediately detecting erroneous data distribution on the data transmission line. Accordingly, the necessary measures can be taken for repairing the erroneous data distribution on the transmission line, and thus when all of the data transmission stations are changed to be connected to a given data transmission line, due to the malfunction of the data transmission line, the correct line connections can be achieved.